1. Field of the Invention
The present invention relates to a heating apparatus having an electrostatic adsorption function, and specifically to a heating apparatus having an electrostatic adsorption function which is used suitably for a heating process of a semiconductor wafer, including a temperature rising process, in the production process and the inspection process of a semiconductor device or the like.
2. Description of the Related Art
Conventionally, a heater where a metal wire is coiled has been used for heating a semiconductor wafer in the production process of a semiconductor device. However, when such a heater is used, there is the problem of metal contamination to the semiconductor wafer. Therefore, in recent years, there was proposed the use of a wafer heating apparatus united with ceramics where a ceramic thin film was used as a heating layer (see Japanese Patent Application Laid-Open (Kokai) No. 4-124076, for example).
Moreover, an electrostatically adsorbing apparatus is used in a reduced pressure atmosphere for fixing a semiconductor wafer on a heater when heating the semiconductor wafer, and the material therefor has shifted to ceramics from resins with a tendency of higher temperature processes (see Japanese Patent Applications Laid-Open (Kokai) No. 52-67353 and No. 59-124140).
Recently, there was proposed wafer heating apparatuses having electrostatic adsorption functions wherein the wafer heating apparatus united with ceramics and the electrostatically adsorbing apparatus are combined. For example, an apparatus wherein alumina is employed for an insulating layer of the electrostatically adsorbing apparatus is used in a low-temperature range such as an etching process (see New ceramics (7), p49-53, 1994.). And an apparatus, wherein silicon nitride, sialon, or aluminum nitride is employed for an insulating layer of the electrostatically adsorbing apparatus (see Japanese Patent Application Laid-Open (Kokai) No. 2001-189378, for example), or pyrolytic boron nitride is employed for an insulating layer of the electrostatically adsorbing apparatus (see Japanese Patent Applications Laid-Open (Kokai) No. 4-358074, No. 5-109876, No. 5-129210, and No. 7-10665), is used in a high temperature range such as a CVD(chemical vapor deposition) process.
Such a heating apparatus having the electric adsorption function is set and used in a semiconductor process chamber. For example, when heating a silicon wafer by using this heating apparatus having the electric adsorption function, first, a silicon wafer is carried into the process chamber with a transfer arm, and the silicon wafer is placed on the heating apparatus having the electrostatic adsorption function.
Next, the silicon wafer is heated by charging a heating layer with electricity while the silicon wafer is adsorbed to the heating apparatus by applying a voltage to an electrode for electrostatic adsorption. After the silicon wafer is heated to a predetermined temperature, processes of annealing and etching, or growing a film by sputtering, CVD or the like are performed.
After the silicon wafer is subjected to desired processes, the power supply for the heating layer is turned off so that the silicon wafer is cooled. After the silicon wafer is cooled to a predetermined temperature, the power supply for the electrode for electrostatic adsorption is turned off, and the silicon wafer are pulled by using a lift pin or the like from the heating apparatus having the electrostatic adsorption function. After that, the silicon wafer is carried outside the process chamber with the transfer arm.
However, in the case of heating/cooling a silicon wafer by using the heating apparatus having the electrostatic adsorption function as described above, since a linear expansion coefficient of the insulating layer of the heating apparatus having the electrostatic adsorption function is different from that of the silicon wafer, each thermal expansion volume and thermal contraction volume of the insulating layer and the silicon wafer are different from each other in a temperature rising and falling process. Thus, they rub against each other.
And, although Vickers hardness of the silicon wafer is about 11 GPa, Vickers hardness of alumina, silicon nitride, sialon, and aluminum nitride, which are used as a material of the insulating layer, are 15 GPa, 16 GPa, 16 GPa, and 14 GPa, respectively. Therefore, in the heating apparatus having the electrostatic adsorption function, wherein alumina, silicon nitride, sialon, or aluminum nitride which are harder than the silicon wafer is used for the insulating layer, there is the problem that the surface of the silicon wafer is ground by the insulating layer when heating/cooling the silicon wafer, then particles are generated, and moreover, scratches are generated on the surface of the silicon wafer. Particularly, in the case that the silicon wafer is heated to a medium and high temperature range of 500-800° C. or a higher temperature range for processing, the difference in thermal expansion volume between the insulating layer and the silicon wafer is further increased, so the particles are further easily generated, and moreover, the scratches are remarkably generated on the surface of the silicon wafer, so that the flatness of the silicon wafer is degraded.
And, as described above, if the particles are generated in the processes such as annealing and etching, it causes the generation of pattern defects and the like in the subsequent device fabrication process, and leads to various problems such as lowering device yield and degrading reliability of devices.
On the other hand, in the case of the heating apparatus having the electrostatic adsorption function, which uses pyrolytic boron nitride for the insulating layer, pyrolytic boron nitride has small Vickers hardness of 2 GPa, which is softer than the silicon wafer. Therefore, there are few cases that the surface of the silicon wafer is ground by the insulating layer when heating/cooling the silicon wafer as described above. But on the contrary, there is the problem that the surface of the insulating layer is ground by the silicon wafer, so that the particles are generated as in the above.